Automatic regulating system



Jan. 8, 1946. R. v. HOWARD 2,392,334

AUTOMATIC REGULATING SYSTEM Filed July 19, 1944 2 Sheets-Sheet 1 A 00/0OUTPUT INVENTOK 19w 2 360 A BY W i i d/V1010?! 477081147 R. v. HOWARDAUTOMATIC REGULATING SYSTEM Filed Ju'iy 19, 1944 2 Sheets-Sheet 2 mm? M.INVENTOR. 2 1 50wwu JDd/V/ 0100 V Patented Jan. 8, 1943 UNITED STATESPATENT OFFICE AUTOMATIC REGULATING SYSTEM Royal V. Howard," SanFrancisco, Calif. Application July 19, 1944, Serial No. 545,101

9 Claims. (01.179-171) My invention relates broadly to amplificationsystems and more particularly to an automatic gain control circuit foramplification systems.

One of the objects of my invention is to provide a circuit arrangementfor an amplifier system in which changes in condition of the signalingenergy at the input circuit of the amplifier system may be employed toautomatically control the operating characteristics of the amplifiersystem for maintaining the level at the output circltit of the amplifiersystem substantially cons an I Another object of my invention is toprovide a system of level control in which the amplifier circuit has theinput thereof connected to the input circuit of a gain control amplifierand the, output circuit thereof connected to a limiter circuit with adifferential circuit associated with the-composite output thereof forrestoring the operating condition of the amplifier to counteractchanging conditions in the .input circuit for maintaining the outputleve1 in the output circuit substantially constant. p

A further object of my invention is to provide an electronicallycontrolled compensation system for amplifier circuits whereby changes inthe condition oflevel of the input have minimum efiect upon the level ofoutput.

Other and further objects of my invention reside in the circuitarrangement for the automatic control system for audio frequencyamplifier channels as set forth more fully in the specificationhereinafter following by reference to the accompanying drawings inwhich:-

Figure 1 diagrammatically illustrates one circuit arrangement embodyingmy invention and Fig. 2 diagrammatically illustrates a modified circuitarrangement of my invention.

The advantages in the use-f the circuit of my invention will be apparentfrom the more detions he is receiving, nor can the operator control themif he is able to diflerentiate or correct wave form and energy contentthat the personnel tailed description hereinafter following. I may isunable to integrate or anticipate. Therefore, it becomes readilymanifest that the ideal solution is some device of a purelyelectronicnature that win control and regulate the program to a finer degree thanthat'obtained by manual operation. Such a device permits a maximumutilization of the facilities and provides a more uniform output,eliminates human error to a great extent, and, further, eifects economyin manpower.

This desirable objective is not as easily obtained as might beapparently indicated, for one of the things that any device of thisnature must not do is destroy the dynamic range of program content.Early experiment proved that it was not feasible or practical to putinto use Just a slow operating volume control device,- for this had aconstant rate of decay and, no matter how the constants were selectedthe desired results could not be obtained. It was noted, fromobservation over long periods of time, that what was needed was a devicethat, once regulated in its control, would not deviate in its gainregulation until a certain period of time had elapsed.

Then, if the program material 'was'low, the device would seek slowly, atfirst, to recover the deficiency. However, it is obvious that, once thelost gain has'been restored by the instrument,

it must be on the qui vive for any sudden applications of normal orexcessive level. The device must also have the property of being able toreduce any abnormally high audio level to the applications.

motion picture systems wherein substantially constant level output ishighly important. No matter how skilled or trained operating personnelmay be, it is impossible to obtain maximum utilization of availablefacilities, be they recording, line transmission, or radio transmission,bymanual operation of volume. No matter-ho w judicious and adept the.personnel may be, individual errors, 1 occur due to the operatorssinterpretation of the volume level indicating devices. Nor is itpossible for the personnel to Judge whether the positive peaks ornegative peaks are causing the indies-1 It was determined by extendedresearch and measurements in standard broadcast practice that veryrarely do program levels vary over a :10- db; Practical applicationsindicate that such a device in a radio transmitter shouldbe placed in acircuit before the, normal peak limiting amplifier, for this enables theconstant use of the limiting amplifier at its maximum efliciency. It isofcoursepossible and practical to incorporate the peak limiter into the'automatic device. y

'The amplifier system that is arranged between the inputvandoutputcircuits of the audio frequency channel has the gain control orguardian bleeder (3.0 megohm) resistor Rn.

circuit at my invention connected substantially in parallel therewith sothat the audio frequency variations which are supplied to the amplifierchannel are also supplied to the input of the gain tion of values) dueto the large size condensers,

restoration of signal would naturally result in an excessive outputlevel for an appreciable period. The deleterious effect is overcome in'the autocontrol circuit. The gain control circuit has the 5 matic systemof my invention by the use of a fastoutput thereof connected to the biascontrol circuit of the tubes oi the main amplifier system and also to aresistance capacity network havinga time constant which is determinativeof the time control, or limiter device. This consists of the tube, inthis particular-case marked SSR'I or 613.1, coupled to the output of themain amplifier or output stage. The diodes ofthis GSR'I or SR! gain rateof the main amplifier. I also provide'lo tube. system are biased at sucha level that it a limiter circuit having its input connected with theoutput of the main amplifier system and connected to the resistancecapacity network for the purpose of restoring the normal condition inthe resistance'capacity network for counterbalancing input control canbuild up to the opposite eflects produced therein by program failure orgain reduction. That is to say,. the resistance capacity networkoperates as a differential circuit controlled in one condition acothercondition according to the output program level. By the coaction oi. thegain control am; plifier with the main channel amplifier a d with theresistance capacity network and the limiter contributes no output duringnormal level operation; This limiter action therefore is to preventexcessive output levels. Its action applies voltage back through 8H6--23until such a time as the its proper operating potential. 1

An adjustable arm marked 8 is provided on resistor Rm which is used toadjust the bias voltage which is connected at point 0 to the tubescording to the input program level and in an- 6SN|2. If the level is toohigh or too-low, the

negative bias may be regulated by adjustment of tap 8 on resistor Ric.

'Meter Mi, shown in the circuit, is used as an indicating device that iscalibrated to show the I am enabled to control with great precision them t of regulation-of gain t t has t k program level supplied to theaudio output circuit.

The system of my invention operates in such a manner" as to maintainessentially a constant audiooutput regardless of variations to the inputlevel between certain desired limits. This control may be accomplishedby utilizing the average level of rectified input signal asj the controlvoltage on an input stage containing variable MU tubes,

' as shown on the diagram. In the particular amsuiting D. C. potentialis sumcient to control the 40 tenuation range of R1.

variable MU 8K|- l2 stage. The tubes marked 81-16- 2 and GHQ-'4 areutilized to obtain a difierential potential which charges condenserslabeled C1 and Co at diflerent potentials: Con- 01 the voltage dividermade up of the 0.5 and 1.0 megohmresistors Rio and R16 locatedbetweenlHt-l and GHQ-2. Now as long as the potentialon Ca exceeds thaton C1, the amplifier gain can not be increased as condenser C1, nothaving a bleeder circuit, holds the charge. If, however, the averageinput signal level to the, OHS-4 decreases, the charge on Co will leakoil! through its When'this potential is reduced to a value below that ofC1,

diode BH6--.I conducts the charge accumulated main unchanged as itrequires this interval oi,'

time for the charge on condenser Co to leak oi! to:a value equal to thecharge on condenser Cm.

for a period exceeding 10 seconds, the gain in the ainplifier will beslowly restored toward a maximum. Since the control device isessentially a slow-time device (the time can be adiusted to any desiredamount by the proper selecplace at any given time. I- provide aresistance network in series and shunt with meter M1 as shown at R0, R1and Ra as required.

The upper section shown in the diagram comprises the main amplifier. Itis represented as a mal input levelis intended to be about 20 db.

below standard reference level of 1' milli-watt in -.600 ohms, Theminimum input level at which it will operate is approximately 25 db. Thehighest input levelpermissiblawill depend on the at- Normally theamplifier operates 10 dbsbelow its maximum possible gain 5b as to permitan automatic increase of 10 db. when the input level denser Ca receivthe higher potentialrbymeans 45 should drop" that amount. In theopposite direction the output remains essentially constant with anincrease of 10 db. above the normal input level resulting in a controlof i 10 db. or total range,

' at I leading through transformer T1 to the potentiometer system R1grounded at 2 and then to the coupling system comprising condensers Cland C: and resistors R2 and R: to the input circuits of v tubes OK'l-land SKI-2.- The cathodecircuit s desired period of Ii, however, theinput signal ceases or is reduced the gain control amplifier formed, bypairs of.

tubes which may be of the types represented at ISNl-l and lSN'|--2. Thecoupling between the.

tube stages is of the resistance capacity type constituted by resistorsRio. Rn. Ru and R1: interconnected by condensers C: and 04 as shown.

The tubes of'thefirst stage have their-cathodes connected to groundthrough resistor R while the tubes of the second stage have theircathodes connected to ground through resistor R14. The output of thesecond stage of amplification connects to the. transformer T3, thesecondary of which connects to the double diodes represented 'at GHG-l,GHB-Z and 6H8--3. The output of the double diode SHE-l is coupled to thesucceeding diode 6116-2 and 8H8-3 through the The power supply systemincludes transformer T0 connected to suitable source of power such as110 volt 60 cycle alternating. .current through fuse potentiometersystem RllivRl6 shunted by conof the double diode BHG-Z as shown. Theanodes of this double diode connect to the anode and cathode of onesection of the double diode 6H63 as shown, the cathode thereof having aresistor R'ze in series therewith as shown. The other section of thedoubl diode 6H63 represented at D4 connects to the resistance-capacitynetwork which includes condenser C1 and condenser Co shunted by resistorR11. a point in the circuit between diodes SHE-2 and 6H63 to themidpoint l2 between resistors R2 and R3 in'the coupling circuit of themain amplifier System. The program level control circuit 5 provides thevariable bias for the control grids of the 6K1 tubes.' It is importantthat condenser C1 has no leakage as it must hold its charg until thevoltage on condenser Ce leaks down to a value equal to that on condenserG1, at which time the gain increase rate of the amplifier is determinedby the timeconstant of condenser Ca and resistor R11. .This'actionoccurs approximately 10 seconds after program failure. During the 10Vsecond period no gain change takes place.

-.The center right section shown at 6 is the limiter circuit. Thi isnecessary to hold the peaks down to normal level until the slow timecontrol circuit has had suflicient time to seek itsnormal operatinglevel. .This limiter acts only for two or three seconds at the beginningof'program. The limiter includes input transformer Ts which connects tothe audio output system on the secondary side of transformer Ta. Theoutput of transformer T5 has a potentiometer R thereacross connectedthrough adjustable tap to the input of the limiter tube GSR'I or 6R1.

system T4 connects from tap it to the diode D4 leading to the resistancecapacity network for restoring the charge to the condensersCa and A tapI0 is taken from F1 and S1. Transformer Tc includes'secondary windings25, 2'6 and 21. Winding 28 supplies heating current for all of theheaters of the heater type tubes.

indicated at 80 or 5Y3. The anodes of the double rectifier tube areconnected to opposite ends of secondary winding 26. .The output of thedoublerectifier connects to the transformer circuit including condensersCa, Ca and C10, and adjustable resistor R1: and inductances L1 and L2.The potential divider across the-output of the power supply system-contains resistors R19, R20 and R21 connected in its positive end tothe anode supply cirv cuits in the gain control amplifier and limiterand at its negative and to ground indicated at 28. The

adjustable tap 29 on the potential divider R20 con-,

tubes SKI-f4 and SKI-2.

Adjustment procedure It is assumed that all tubes are operatingproperly. Set R1 about 16 db. below maximum gain. Set Ras for zeroinput. Potential dividerRn is selected of a value for obtaining maximumpositive potential on the SHE-l cathode through adjustable tap 29 onpotential divider R20. Now adjust Rs until M1 reads full scale. If thiscannot be accomplished the value of .Ra should be altered. Now feed a400 cycle audio signalinto the am-' plifler input at a level of about-20 db. below standard reference. Now reduce the positive bias on tube6H6-.-l by means of adjustable tap 29 on potential divider R20 until M1just begins to show a current reduction. Now increase the gain 10 db. bymeans of R1. M1 should now show ap proximately mid scale.- Theadjustment of Ru can only be made approximate by means of a steady tone.A volume indicator should be connected across the output before theladder attenuator as the level is rather low. Now increase the audiooscillator output of the volume indicator about 10 db. and observe theoutput level. Ric should be. adjusted until the output level shows areduction of approximately -3 db. If it were not for the action of thisnegative bias on OSNI-J, the amplifier would be over controlled.

- The proper adjustment of this bias can only be made with actualprogram material feeding in as will be explained later. There remainsthe adjustment of B25. Feed an audio signal in just sufilcient to startcurrent reduction on M1. Now remove GHS-l from socket. Increase thesignal input 4-db. Now adjustRrs until M1 just begins C1. Th currentthrough this circuit is reguwhen the entire system is operatingnormally.

to show current reduction again. This will be the proper adjustment.

Now for actual adjustment under program con- I dition's. An attenuatorcapable of 20 db. range should be inserted in the input to theamplifier.

and some program material connected to the input to the attenuator. Setthe attenuator for 20 db. loss and adjust R1 until M1 just begins toshow level 10 db. After several seconds-M1 should show: about mid scaleand the output level should show the same level as previously noted. Nowincrease the input level another 10 db. and after several seconds notethe output level. If the level is too Winding 21 supplies heatingcurrent forthe cathode of the double rectifier tube C 4 mi. paper, 600volt 4 V high provide less negative bias for GSNl-2 by means of R18. Ifthe level is too low, increase this bias. It may be necessary to makefurther adjustments of R21 and repeat the above procedure in order tosecure a linear dynamic control characteristic which shows constantoutput with a total input variation of 20 db. The 6H6 tubes arepreferablyglass in order to'reduce leakage.

I have listedhereinafter the values for the several circuit componentswhich I have found most.

efiicient for carrying out my invention in the circuit of Fig. 1:

Ra Approximately 200 ohm, depends 011 meter used R a 1500 ohm, 1 wattR10 10,000 Ohm, 1 watt R11 10,000 ohm, '1 watt 500,000 ohm, /2 watt500,000 ohm, /2 watt 1000 ohm, 1 watt 500,000 ohm, watt 125,000 ohm(regular volume control) 3 mega, /3 watt 2000'ohm wire wound 20 watts,slide wire 5000 ohm wire wound 20 watts 5000 ohm wire wound, slide wire,10 watts 100 ohm wire wound 250,000 ohm, /2 watt 1500 ohm, 1 watt 75,000ohm, 1 Watt 1 meg. (regular volume control) /2 meg, /2 watt .01 mi. micacondenser .01 mi. mica condenser I .05 mi. paper condenser, 600volt .05mi. paper condenser, 600 volt '2 mf. paper condenser, 400 volt 2 mi.paper condenser, 400 volt C7 A; mi. Pyranol, 600 volt Cs 4 mi. paper,600 volt or equivalent electrolytic condenser C9 4 mf. paper, 600 voltor equivalent electrolytic condenser R13 R14 R15 R16 R17 R18 R12 R20 R21R22 R23 R24 R25 R28 C1 or equivalent electrolytic condenser C11 .1- mf.,400 volt paper condenser C12 25 mv., 150 volt electrolytic condenser T1Well shielded input transformer, line to grid,

good quality T2 Output transformer, approximately 10,000

ohm primary to 500 ohm secondary T3 Approximately 20,000 ohm primary,one to one ratio overall T4 Approximately 10,000 ohm primary, ratioprimary to one-half secondary one to one Referring to Fig. 2 of thedrawings it will be seen that the voltage from transformer T-3 is fed tothe tube labeled GHG-l. The rectified output of tube liH6---l isimpressed across con- R15 and R16.

denser C5 which has shunted across it resistors sistor identified as R26to the control line l0, connecting to point l2 intermediate resistors R2and R2. The other cathode of SHE-2 is connected at point 8 of R16 whichis adjustable. The other plate of tube SHE-2 shown at D-4 is connectedto thecontrol circuit l0 which is connected to ground via a one-halfmicrofarad condenser identifled as C7.' The limiter circuit derives itsvoltage from 6K|-l and 6K1-2 which is applied through suitable blockingcondensers to the grids of tube 5SN1--3 whose plates are coupled to anoutput transformer labeled T4 whose secondary is coupled to' tube SHE-4.The output of this circuit is connected to a stabilizing resistor. R2;to diode D6 of tube 6H63 in the arrangement shown in Fig. 2', whose lateis connected to control circuit l0. v i I A connection is made at thecathode of tube "SHE-4 of diode D--l whichconnects with the cathode ofdiode D5 of tube 6H6'3. The plate of diode D-5 is connected throughresistors R31- and Rza tothe cathode of tube 6SNl-3. Voltage is receivedfrom the output of tube .6H8--l which charges condenser Cs which hasconnected across-it resistors R15 and R111. Voltage is picked up fromthe adjustable divider at connection 8 on R16 which is impressed uponthe cathode of D& of tube 6H6-2 which is then passed on via the plate ofdiode section D-d upon C5 is reduced by the action of the shuntingresistors R15 and R16 to a point where its voltage is less than that ofC1 of control circuit 80, then diode D--3 of tube 0116-2 conducts andthe voltage across Cris reduced by the resistance of D-S and the othercircuits and the decay charbias is obtained by the voltage dropoccurring acteristics of this voltage are determined by re sistors RaR16 and the resistance or diode M of tube 0H6-2. By such action thevoltage on control circuit l0 connected to the control tubes is furtherreduced. and the gain of the controlled amplifier is increased. 'With nosignal impressed on the output of the diodes of tube 6118-4 the of tubeGHQ-3 and resistors R31, R21 and R112 T5 Input transformer, line togrid, 500 ohm to whose voltage is adjusted on. Ruby variable connectionR32 therefore increasing the rate of control'through control circuit l0.

The center right section shown at 0 is a limiter circuit. This isnecessary to hold the peaks downto'normal level until the slow-timecontrol circuit has had suflicient time to seek its normal operatinglevel. This limiter acts for approxi The voltage from 6H6-i plates tion.

reslstorRai. However until it is made inoperadiodes, a limiter circuithaving lament-e9 tive, voltage is developed in the output circuit oftube lSN'l-3 which is fed to the cathodes of tube OHS-4 throughtransformer T4 through the load of the terminating resistor R2: to diodeD-.8

of tube 6H6-3. The output of diode D-G is 1 connected to control circuitI0. This voltage is D 6 also reduces the voltage on the grids of 1 tube6K'|- l2. 1 The fixed bias on diodes SHE-4 is supplied by tap 29 ofpotentiometer R20.

This bias regulates the point at which the operation of diodes of tubes8H6l will come into operation.

I The peak limiter is definitely made inactive until slow-time controlbecomes inactive. The circuit of Fig. 2 has ,a finer limit of control.On this instrument the outputvoltage'becomcs linear after the controlsection has reached saturanected with the output of said audiofrequencyamplifier channel, a connection between'the out put ofsaid limitercircuit and said condensers, and means interconnecting one of said condensers and said bias control circuit for correctlng the bias condition.of said audio frequency amplifier system to compensate for variationsin level of the program incident upon the input circuit of said'audiofrequency amplifiersystem.

2. In a system for controlling amplification level inaudio frequencyamplifiers in combination an audio frequency amplifier channelinchannel, a condenser circuit having a substan- The components of thecircuit of iig. 2 are substantially the same as'set forth in Figure lwith the addition of the components illustrated in Fig. 2 which havevalues as follows:

meg., /2 watt /2 meg., /2 watt 1000 ohms, 1 watt 5000 ohms, 1 watt 1meg., 1 watt C14 .05 mi. mica condenser C15 .05 mf. mica condenser tialtime delay discharge rate connected with the output circuit of said gaincontrol-amplifier, a

charge accelerating circuit connected between said main amplifierandsald gain control ampliand R3 to meg. It will be understood, however,that I have made reference herein to val ues merely for the purpose ofexplaining certain preferred embodiments of my invention and that I haveno desire to restrict the components to the particular values shown. Asheretofore noted the control system of Fig. 2 is in certain.

installations more effective than the control sysmm of Fig. 1 as thecircuit of Fig. .2 exerts a and types of the circuit components and Iintend no limitations upon my invention other than may be imposed by thescope of the appended claims. What I claim as new and desire to secureby Letters Patent of the United States is as follows: 1. In a system forcontrolling amplification level in audio frequency amplifiers incombination an audio frequencyamplifier channel ineluding an inputcircuit, an output circuit and a bias control circuit, a gain controlamplifier having its input circuit connected with the input circuit ofthe aforesaidaudio frequency ampli-' fier channel, pairs of diodesconnected with the output circuit of said gain control amplifier, 'a

condenser connected with the output of one of said diodes, 'a condensershunted by a resistor connected with the output of the other of saidmentioned network and the bias control circuit fier, a multiplicityof-isolating diodes connected with the output of said gain controlamplifier, a

resistance shunted by a condenser connected with one of said diodes, acondenser connected with the other of said diodes, a limiter circuitconnected with the output of said main amplifier, and circuitconnections between said diodes, said condensers, said limiter circuitand between said condensers and said bias control circuit for flu--pressing bias potential upon the bias control circuit of said mainamplifier proportional to changes in the operating conditions in theoutput circuit of said main amplifier.

4. A control system for amplifiers comprising in combination with a mainamplifier including a bias control circuit therefore,-a gain controlamplifierhaving a bias control circuit, means for simultaneously feedingboth said main amplifier and said gain control amplifier, a multiplicityof isolating diodes connected with the output of said gain controlamplifier, resistance capacity networks connected with each of saiddiodes, a connection between one of said networks and the bias controlcircuit of said gain control amplifier, a connection between another ofsaid networks and the bias control circuit of saidmain amplifier, and alimiter circuit interconnecting said last of said main amplifier. 5. 'Acontrol system comprising an amplifier having an input circuit. a biascontrol circuit and an output circuit, a gain control amplifier havinginput, bias control and output circuits, a parallel feed circuit foreach of said input circuits, a dif- .ferential control circuit connectedwith the output circuit ofsaid gain control amplifier, a limiter circuitconnected between the output of said main amplifier and saiddifierential circuit, and con- .nections between said differentialcircuit and the bias control circuits of said main amplifier and saidgain control amplifier for determining the bias potential on said mainamplifier by the con- 8, A control system comprising an amplifier .jointaction of said gain'control amplifier-and saidlimiter circuit upon saiddifierential circuit. 6. A control system comprising an amplifier havingan input circuit, a bias control circuit and an output circuit, a gaincontrol amplifier having input, bias control and output circuits, 9.parallel feed circuit for each of said input circuits, a capacitativecircuit connected with the output circuitof said gain control amplifierand operative to' be discharged thereby according to decay in thecurrent supplied to said input circuits, a connection from saidcapacitative circuit to the bias con& trol circuit of said gain controlamplifier, a connection from said capacitative circuit to the biascontrol circuit of said first mentioned amplifier,

and means interconnecting said capacitative circuit with the outputcircuit of said first men-' tioned amplifier for restoring the, chargedcondition of said capacitative circuit and maintaining predeterminedbiased condition of the bias circuit of said first mentioned amplifier.

. connection from said capacitative circuit to the bias control circuitof said first mentioned amplifier, a limiter circuit comprising aresistance having an input circuit, a bias control circuit and an outputcircuit, a gaincontrol amplifier having input, bias control and outputcircuits, a parallel teed circuit for each oi'said input circuits, acapacitative circuit connected with the output circuit'oi said gain'control amplifier and operative to be discharged thereby according todecay'in the current supplied to said input circuits. a connection fromsaid capacitative circuit to the bias control circuit of said gaincontrol amplifier, a connection from said capacitative circuit to thebias control circuit of said first mentioned amplifier, a resistancenetwork, means for in combination with a main amplifier including a"networkconnected with'the output of said first mentioned amplifier, andan accelerating amplifier connected with said resistance network withthe output thereof connectedto said bias control circuit foraccelerating the restoration of said bias control circuit to apredetermined normal operating condition.

capacitatively connecting said resistance network to the output circuitof said first mentioned amplifier, and an accelerating amplifierconnected with said resistance network and connected with said biascontrol circuit for restoring said bias control circuit to apredetermined bias control condition. y

9. A control system for amplifiers comprising bias control circuittherefore, a gain control amplifier having a bias control circuit, meansfor simultaneously feeding both said main amplifier and said gaincontrol amplifier, a multiplicity of isolating diodes connected with theoutput of said gain control amplifier, resistance capacity networksconnected with each of said diodes, a connection between one of saidnetworks and the bias control circuit of said gain control amplifier, aconnection between another of said networks and the bias control circuitof said main amplifier, a resistance network, means for capacitativelyconnecting said resistance network with the output of said firstmentioned amplifier, an

- electron tube acceleratingcircuit connected with said resistancenetwork and connections from said electron tube accelerating circuit tosaid bias control circuit .for expediting the restoration of ROYAL V.HOWARD

